When an alternating current voltage is converted by a rectifier into direct current voltage, a certain amount of ac ripple is left over in the resulting rectified dc voltage. In the electroplating industry, 3 phase rectifiers are often used to produce the necessary direct current voltage for the electroplating process. Failure of such a rectifier is often partial, resulting in an increased and potentially damaging load on the remaining working components of the rectifier and increased ac voltage ripple. Increased ripple can adversely affect the quality of products made by the electroplating process. Printed circuit boards are especially sensitive to increased ripple during the electroplating process. Moreover, partial failure of the rectifier is often difficult to detect until the product is examined and found to be defective.
A ripple meter provides a means for detecting and monitoring the percentage of ripple in a direct current voltage. When the meter indicates a percentage of ripple above acceptable levels, the problem may be addressed immediately. Such a warning serves two purposes. First, if the dc rectifier is at fault, it may be repaired before the increased load on the working components burns them out. Burn out of additional dc rectifier components could substantially increase repair costs. Second, the problem may be addressed before a substantial amount of electroplating product is ruined by high levels of ripple.
The prior art shows various devices for detecting a ripple component of a dc voltage, but, at best, they merely compare the ripple component to a reference voltage independent of the input voltage. They do not display a comparison of the ripple component to the input voltage as a percentage of the input voltage.
Showing the ripple voltage as a percentage of the input voltage is advantageous for certain applications, such as for monitoring an electroplating voltage produced by a 3 phase rectifier. The voltage of an electroplating rectifier may be changed from one batch to the next without readjustment of the meter since the same percentages of ripple are often acceptable from batch to batch even though the electroplating voltage has changed. However, where ripple voltage in an electroplating rectifier voltage is measured against a reference voltage, the reference voltage must be reset each time the rectifier voltage is changed.
For example, U.S. Pat. No, 4,242,674 to Wheeler relates to a detector for triggering an alarm when the alternating current component of the mainly dc current output produced by an aircraft alternator with solid state diode rectifiers reaches a predetermined level symptomatic of incipient failure of some component of the alternator or rectifier. Wheeler does not measure or indicate a ripple percentage of the output voltage. Rather, an alarm is activated when any significant ac ripple exists in the dc voltage.
U.S. Pat. No. 4,520,310 to Kelly et al. relates to a voltmeter automatically switches from ac mode to dc mode and vice versa when an ac component reaches a predetermined threshold. Absolute voltages are measured by the device, and reference voltages are set to establish values to initiate switchover from mode to mode. The device may also indicate that an ac ripple component exists with dc voltage, but does not indicate the percentage that the ripple represents.
U.S. Pat. No. 4,694,193 to Schlenk, et al. relates to a fault recognition current for parallel power supply devices. It compares separate reference voltages to each of the ac and dc voltage components of an input voltage from a set of parallel power supplies to detect failure of at least one power supply out of the set of parallel power supplies.
U.S. Pat. No. 3,210,603 to Calfee, et al. relates to a generator protector which detects increases in ripple current in the output voltage of a brushless alternating current generator and shuts down the exciter field in response thereto. The percentage of ripple is not detected or shown by this device.